A border crosser is captured after crossing the Rio Grande river from Mexico into the U.S. in Rio Grande City, Texas. / Michael Chow, The Arizona Republic

by Bob Ortega and Rob Oâ??Dell, The Arizona Republic

by Bob Ortega and Rob Oâ??Dell, The Arizona Republic

RIO GRANDE CITY, Texas -- The load wasn't hard to spot. Officers could see the marijuana bundles peeking out from the back of the SUV. But, as they pulled behind it, the driver turned to follow a school bus dropping off children.

"They take advantage of the school traffic. ... They know we won't initiate a stop when there are students around," said Nat Gonzalez, an investigator for a multiagency drug task force in Starr County, Texas.

Stop by stop, on that Monday earlier this month, the officers followed, watching the driver make calls on his cellphone, until he swerved south toward the Rio Grande.

Before they could catch up, he jumped out, sprinted for the river and swam to Mexico, leaving 1,400 pounds of marijuana behind.

The cartel smugglers know a great deal about how law enforcement here operates, and they have turned the Rio Grande Valley into one of the busiest marijuana corridors in the United States. Texas still trails Arizona in the volume of pot being seized by the Border Patrol and Customs. But if there's one part of the Southwestern border that illustrates the challenges of combating marijuana smuggling, it is along the winding river here.

Last year, across the Southwest, the Border Patrol, Customs and Border Protection and other law-enforcement agencies intercepted more than 3.5 million pounds of marijuana - nearly a fifth of an ounce for every person in the United States.

But in the Rio Grande Valley, for every load they capture, 10 slip through, local officials estimate. Federal law-enforcement officials agreed.

The loads get through because the drug cartels closely monitor the Border Patrol and other law-enforcement agencies. The cartels study their tactics and strategies, and adapt quickly. They use that knowledge and the corrupting influence of money to win the daily cat-and-mouse games that define drug smuggling across the Rio Grande.

Encounters between agents and drug smugglers are frequent but rarely lethal. When cornered, drug runners are likely to abandon the loads of marijuana and escape back across the river.

Nationwide, nearly every drug-smuggling case in which Border Patrol agents did report responding with force over a 29-month period involved marijuana, The Arizona Republic found. Force can include using firearms, physical force, less-lethal weapons and devices to stop vehicles, like tire spike-strips.

The Republic reviewed more than 12,000 pages of CBP and Border Patrol use-of-force incident reports, obtained through the Freedom of Information Act. The reports covered 2010 through mid-2012.

That data shows marijuana smugglers run into the Border Patrol not just at highway checkpoints, but during frequent, small-scale runs crossing the border between ports of entry. By contrast, drugs such as cocaine, heroin and methamphetamine seem to be caught primarily at official ports of entry or at highway checkpoints. Only two use-of-force incidents involved the smuggling of hard drugs.

The incident reports show that the Rio Grande Valley, where the river meanders so sinuously that it creates coils of U.S. territory nearly surrounded by Mexico, offers fertile soil for marijuana smuggling.

Last fiscal year, the Border Patrol said it seized 797,000 pounds in the Rio Grande Valley Sector. That trailed only the Tucson Sector's 1.2 million pounds; seizures in the Rio Grande sector totaled more than in the remaining 18 Border Patrol sectors combined. The sector covers 320 miles of the Rio Grande westward from the Gulf Coast.

Border Patrol officials in both Texas and Washington, D.C., declined to answer specific questions for this story. But Border Patrol Chief Michael Fisher told an audience in Phoenix during a border-security conference two weeks ago that south Texas has become the most active area along the border and is tops in terms of weight of marijuana per seizure.

Border Patrol figures showed a 10 percent drop in marijuana seizures by agents in the Rio Grande Valley Sector from a year before, but south Texas drug authorities said they aren't seeing any decline.

"We think we're seeing an increase," said Carlos Garcia, Starr County's coordinator for Operation Stonegarden, a Homeland Security-funded program that provided $55 million last fiscal year to help pay local law-enforcement border-security costs. Garcia said seizures and incidents of loads being dumped are rising.

"In 30 seconds, they'll load a thousand pounds into the bed of a pickup," he said. "There can be 10 to 15 guys swimming across the river with loads on life rafts."

Same spiking story

A clear picture of the quixotic effort to stop marijuana smugglers in the Rio Grande Valley emerges in the many use-of-force incidents here in which agents used tire-deflation devices to try to apprehend smugglers they saw loading vehicles with bundles of marijuana.

Report after report repeats the scenario.

Agents spot smugglers at the Rio Grande loading bundles of marijuana into a vehicle, usually an old pickup truck, SUV or van. Border Patrol agents give chase and get authorization to "spike" the vehicle with a controlled tire-deflation device.

The smugglers bail out, often in a strategic spot, and flee. Agents find the vehicle with the load inside. The Border Patrol confiscates the vehicle and its load and announces that hundreds of thousands of dollars of drugs have been taken off the street.

But a search for the smugglers comes up empty. By the time the agents seize the drugs, the smugglers either already have swum back to Mexico or are on their way.

Incidents like this occurrednearly 50 times along the Rio Grande in south Texas between 2010 and 2012, CBP use-of-force reports show. There were fewer than 10 such incidents along the rest of the Southwest border.

In nearly every case, the driver and passengers escaped and the Border Patrol agents, following agency policy, stayed with the marijuana. Gonzalez, the Starr County task-force investigator, said other law-enforcement agencies do the same, to prevent smugglers doubling back and taking off in the vehicle again.

A river runs through it

At dusk one recent evening, a Border Patrol helicopter circled over a spot on the river just below downtown Rio Grande City. Three men in dark clothing paddled vigorously across the river in an inflatable boat, turning back toward Mexico. The river is narrow enough here, perhaps 60 yards across, that it takes scarcely a minute to cross.

A few minutes later, the bobbing flashlight of a Border Patrol agent approached across a quarter-mile-wide field. The agent pulled up a barbed-wire strand to let a handcuffed migrant he had caught slide under to the heavily rutted dirt road where the agent's vehicle was parked, lights flashing.

The agent, who was reluctant to talk and asked not to be identified, said migrants tend to cross the river in or near town, and the drug smugglers out of town.

"This is what it's like all the time, any hour," he said, nodding to his flashing lights and the helicopter, still overhead.

Gonzalez, the Starr County HIDTA task force investigator, said, "At night, downtown, every night you can hear the helicopters. It's normal. It's like hearing the train."

Behind his office sits a huge impound lot, ringed by tall fences topped with barbed wire, where some 200 vehicles seized in several months of drug raids await auction. A shiny Chevrolet Camaro that looked fresh off the dealer's lot faced a bulldozer and a backhoe. He showed trucks with fake signs for Texas businesses. There were boats, trailers, and - this being south Texas - row upon row of pickups and SUVs.

Gonzalez squatted next to one SUV to point out how the frame and springs have been welded "so it doesn't ride low when it's fully loaded." The rear seat had been removed to add space for drugs. Black paint coated the inside windows; from outside, they merely looked tinted.

"They'll use anything, good cars, ugly cars, anything to get it through," Gonzalez said.

After a short drive, he parked near the Rio Grande and led the way down a steep dirt trail to a spot on the bank. The deflated husk of a raft, slashed by agents, was nearby.

Heavy brush grows down to the bank on both sides of the winding river, offering endless hiding places for smugglers to wait until the coast is clear, or, on the U.S. side, to stash a load for later pickup. There are scores of small roads on the U.S. side that give access within minutes from the river to U.S. 83, a major east-west corridor.

"We've seen guys, in Starr County, sitting in trees on the Mexican side, watching the fields on this side with big binoculars," Gonzalez said. "They have great communication.

Then, too, sometimes those banking it are officers bought and paid for by the cartels.

In August 2009, former Starr County Sheriff Reymundo Guerra was sentenced to 64 months in prison after being convicted of conspiracy for accepting bribes to help smugglers evade the law. Last year, in neighboring Hidalgo County, nine members of a narcotics team of sheriff's deputies and Mission, Texas, police officers were convicted on charges related to accepting bribes to guard marijuana and cocaine shipments. Friday, Hidalgo County Sheriff Lupe Trevino resigned. He didn't say why, but amid the scandal he's also fighting a lawsuit alleging that he accepted $10,000 in illegal cash donations from a drug dealer.

During 2011 and 2012, Homeland Security's Office of the Inspector General investigated at least 19 Border Patrol agents or CBP officers in the Rio Grande Valley Sector over allegations of drug smuggling, according to records obtained by The Republic. The outcomes of those investigations couldn't be determined.

"There's so much money," Gonzalez said with a shrug. "You really need an active, dedicated officer for this kind of job."

Use of force

The Republic's investigation found that relatively few use-of-force cases involved drug smuggling, compared with human smuggling or illegal crossings. Seven of the 45 killings by CBP and Border Patrol agents since 2005 examined by The Republic involved drug smuggling - and marijuana was the only drug mentioned in those reports.

Out of nearly 1,600 CBP use-of-force reports nationwide from 2010 to mid-2012 The Republic analyzed, fewer than 125 reports specifically mention marijuana smuggling. But many other use-of-force cases had too little information to determine whether they were related to drug smuggling or undocumented migrants.

CBP officials hadn't responded by deadline to an August 2013 public-records request for more recent data.

Dennis Kenney, professor at the John Jay College of Criminal Justice at City University of New York, said there's a good reason marijuana is the main drug in use-of-force reports - more marijuana is smuggled and it is bulkier and harder to conceal than heroin or cocaine.

"If there's more of it and it's more likely to be found, you're likely to have a disproportionate amount of the cases involving marijuana," Kenney said.

The Drug Enforcement Administration and CBP officials declined interview requests regarding the effectiveness of their efforts to interdict marijuana. However, the DEA's Drug Threat Assessment for last year noted that marijuana is increasingly available across the U.S. and is more potent. Independent studies suggest it's also less expensive than five or 10 years ago.

"Looking at the data, I think you'd be hard-pressed to point to anything that shows the drug-control policy has been effective, or that enforcement is doing what it's supposed to do," said Jeffrey Miron, an economist at Harvard University who has studied the market for marijuana.